1. Field of the Invention
The present invention relates to a traffic-light cycle length estimation device for estimating a cycle length that is a time interval from the time the traffic light color changes to green to the time the traffic light color changes back to green via yellow and red.
2. Description of Related Art
A traffic-light information estimation device for estimating a cycle length is proposed, for example, in Japanese Patent Application Publication No. 2009-116508 (JP 2009-116508 A). The cycle length refers to a time interval from the time the color of a traffic light, installed at an intersection, changes to green to the time the color of the traffic light changes back to green via yellow and red. This device estimates the cycle length of a traffic light, based on the time difference between the time a vehicle in the stopped state at an intersection starts moving when the traffic light changes to green and the time a vehicle starts moving at a later time when the traffic light changes to green again.
However, because the device described above assumes that there is always a vehicle that starts moving when the traffic light changes to green, the cycle length cannot be estimated at an intersection where the traffic is light.